The size of the files that are made through Submittal123 is completely dependent on how large the manufacturer's PDF files are to begin with. Our stamps and cover pages add only several kb per page, so nothing that would be noticeable.
So, sadly there is nothing we can do in regard to making your final package smaller. How your computer handles a larger file would be determined by how much RAM your computer has and the program you are using to edit the package. You may want to try installing a trial of Adobe Acrobat Standard, Bluebeam PDF, or another PDF editing program and see how they do at editing the files.
However, Pdf's in general do not do well when they are over 100mb. We have a solution for that. You can build them in pieces in our system.
Click the 'Choose Pages' button at the bottom of the builder screen (after you've clicked 'build package') and only select pieces of the package. If you still need the complete content page you can create that by clicking the 'Content Page as PDF' link at the bottom of the build page. Once you've got all of the package built in pieces, go ahead and put it together in your favorite pdf editor.
If you have Adobe Standard or Pro, you can 'optimize' the package which should shrink it some.
Acrobat Pro also has a Reduce Size function.
Contact our support team with further questions.
Regards!